Superhydrophobic carbon nanotube/polydimethylsiloxane composite coatings

This paper reports a method for fabricating carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite superhydrophobic coatings. With toluene as a solvent, the coating is obtained directly by spray of CNT/PDMS/toluene suspension. The hydrophobicity and micro-/nanostructure of the coatings are studied with respect to the mass ratio (MR) of CNT to PDMS. Based on the multiscale morphology analysis, it is shown that the nanoscale roughness is essential for achieving superhydrophobicity. To form nanoscale rough surface and obtain a stable superhydrophobic coating, MR>0·3 is recommended. In addition, such coatings also show small slide angle, low adhesion strength and long term stability of the coated surface. The method reported in this study is low cost and especially suitable for engineering applications.     

Enhanced thermal conductivity of epoxy nanocomposites filled with hybrid filler system of triethylenetetramine-functionalized multi-walled carbon nanotube/silane-modified nano-sized silicon carbide

Multi-walled carbon nanotubes (MWCNTs) were first treated by a 3:1 (v/v) mixture of concentrated H₂SO₄/HNO₃, and then triethylenetetramine (TETA) grafting was carried out. Nano-sized silicon carbide particles (SiC_np) were modified by the silane coupling agent. Epoxy nanocomposites filled with hybrid filler system containing TETA-functionalized MWCNTs and silane-modified SiC_np were prepared. The investigation on the thermal conductivity of epoxy nanocomposites filled with single filler system and hybrid filler system was performed. Chemical surface treatment is conducive to the enhancement of thermal conductivity of epoxy composites. The thermal conductivity of epoxy composites with hybrid filler system is higher than that of epoxy composites with any single filler system (functionalized MWCNTs or modified SiC_np), which is due to the effective combination of MWCNT-to-MWCNT and SiC_np-to-SiC_np conductive networks. Hybrid filler system could provide synergistic effect and cost reduction simultaneously.     

Ultrasonically prepared polystyrene/multi-walled carbon nanotube nanocomposites

Polystyrene (PS) and multi-walled carbon nanotube (MWNT) nanocomposites were synthesized via an in situ bulk polymerization by employing an ultrasonicator without adding an initiator, in which the ultrasonication was found to do a favor in producing well-dispersed MWNT in the PS matrix. Morphology of the as-synthesized PS/MWNT nanocomposite was investigated by both scanning electron microscopy and transmission electron microscopy. Electrical conductivity of the PS/MWNT nanocomposite film fabricated by a solvent casting method was also examined to be enhanced with MWNT content, while average molecular weights of the synthesized PS in the PS/MWNT nanocomposites analyzed by a gel permeation chromatography increased and then saturated at 2 wt% MWNT. Rheological properties of MWNT containing PS were enhanced because of improved dispersion of the MWNT through an interaction between MWNT and PS.     

Microwave-absorbing properties of silver nanoparticle/carbon nanotube hybrid nanocomposites

Silver (Ag) nanoparticles fabricated by chemical reduction process were grafted onto the surface of carbon nanotubes (CNTs) to prepare hybrid nanocomposites. The Ag/CNT hybrid nanomaterials were characterized using transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. The Ag/CNT hybrid nanomaterials were then loaded in paraffin wax, and pressed into toroidal shape with thickness of 1 mm to evaluate their complex permittivity and complex permeability by scattering parameters measurement method in reflection mode using vector network analyzer. The reflection loss of the samples was calculated according to the transmission line theory using their measured complex permittivity and permeability. The minimum reflection loss of the Ag/CNT hybrid nanocomposite sample with a thickness of 1 mm reached 21.9 dB (over 99 % absorption) at 12.9 GHz, and also exhibited a wide response bandwidth where the frequency bandwidth of the reflection loss of less than ?10 dB (over 90 % absorption) was from 11.7 to 14.0 GHz. The Ag/CNT hybrid nanocomposite with thickness of 6 mm showed a minimum reflection loss of ~?32.1 dB (over 99.9 % absorption) at 3.0 GHz and was the best absorber when compared with the other samples of different thickness. The reflection loss shifted to lower frequency as the thickness of the samples increased. The capability to modulate the absorption band of these samples to suit various applications in different frequency bands simply by manipulating their thickness indicates that these hybrid nanocomposites could be a promising microwave absorber.     

Polypyrrole/multiwall carbon nanotube nanocomposites electropolymerized on copper substrate

Polypyrrole/multiwall carbon nanotube (PPy/MWCNT) nanocomposites were successfully synthesized by electropolymerization of MWCNT-dispersed pyrrole solution on the surface of copper electrodes. The obtained nanocomposites were characterized with scanning electron microscopy (SEM), linear sweep voltammetry (LSV) and thermal gravimetric analysis (TGA). Polypyrrole structures which embraced the MWCNTs led to the formation of nanocomposite striated parallel walls. MWCNTs acted as appropriate substrates for electrodeposition of polypyrrole particulate structures and high yield synthesis of PPy was observed on them. Smooth PPy/MWCNT nanocomposite films were obtained on Cu electrodes by decreasing the potential scan rate. Thermogravimetric analysis showed that MWCNTs increased the thermal stability of polypyrrole.     

Oxidation behaviour of alumina–silicon carbide nanocomposites

Oxidation studies were conducted on Al₂O₂–SiC nanocomposites at 1400 °C. The composites were prepared by hot-pressing mixtures of commercial alumina and ultrafine SiC powders, in amounts of 5, 15 and 30 vol %. Linear kinetics were detected for the oxidation of composites containing 5 vol % SiC. Two stages were observed in composites containing 15 vol % SiC: the first linear and the second presumably parabolic. A parabolic behaviour was observed in the sample containing 30 vol % SiC. The oxidation rates were several orders of magnitude higher than those of monolithic SiC and the observed data were not consistent with the expected increase in weight associated with the oxidation reaction of SiC to SiO₂; in fact the most surprising feature is that the sample containing 30 vol % SiC showed a better oxidation resistance than samples containing 5 and 15 vol % SiC. The reaction products were alumina and mullite in samples with 5 and 15 vol % SiC, while mullite and silica were found on the oxidized surface of samples containing 30 vol % SiC. Explanations are given of the influence of the oxidizable phase amount, the presence of impurities, reaction product structure and composition.     

碳纳米管/聚乙烯咪唑纳米复合材料的制备与表征

采用化学改性手段制备了一类新型的碳纳米管／聚乙烯咪唑(CNTs／PVI)纳米复合材料。并通过红外光谱、扫描电镜、透射电镜和X射线衍射等手段表征CNTs／PVI产物。有机杂环聚合物引入碳纳米管材料体系以后,会显著改善碳纳米管在有机溶剂中的分散均匀性和可加工性,并将碳纳米管具有的优异力学、热稳定性能和杂环聚合物具有的优良溶解性等结合起来,得到一种新型的综合性能优异的光电功能材料。     

Synthesis and characterization of multiwalled carbon nanotube/FeCo nanocomposites

Multiwalled carbon nanotube/FeCo nanocomposites were produced by Catalytic Chemical Vapour Deposition using highly porous FeCo-SiO2 aerogels with different loadings and dimensions of FeCo nanoparticles as catalysts. Multiwalled carbon nanotubes with average number of walls depending on the size of the catalyst nanoparticles were obtained. Inside the nanotubes spherical or elliptical FeCo nanoparticles are retained, and the magnetic properties of the resulting nanocomposites were characterized in detail.     

碳纳米管/聚乙烯复合物分子动力学模拟研究

采用分子动力学方法模拟了碳纳米管/聚乙烯复合物的结构、热力学和力学特性,分析其随模拟温度和碳纳米管填充率的变化。模拟结果表明,碳纳米管/聚乙烯复合物为各向同性的无定形结构,聚乙烯和碳纳米管通过较强的范德华作用结合在一起,在聚乙烯基体作用下,碳纳米管壁上的碳原子排列的周期性下降,出现弯曲和褶皱。从能量上看,填充率较高的复合物更加稳定。碳纳米管/聚乙烯复合物具有比聚乙烯体系更高的等容热容和与聚乙烯体系相反的负值热压力系数,热容随碳纳米管填充率的变化较小,但随温度的升高而明显减小,具有显著的温度效应;热压力系数随温度的变化较小,温度稳定性比聚乙烯更好,但随填充率增加而减小。碳纳米管/聚乙烯复合物的力学特性表现出各向同性材料的弹性常数张量,弹性模量和泊松比比纯聚乙烯体系高得多,并且都随温度的升高和碳纳米管含量的降低而减小,说明加入碳纳米管可显著改善聚乙烯的力学性质。     

Light harvesting with multiwall carbon nanotube/silicon heterojunctions

We report on a significant photocurrent generation from a planar device obtained by coating a bare n doped silicon substrate with a random network of multiwall carbon nanotubes (MWCNTs). This MWCNT/n-Si hybrid device exhibits an incident photon to current efficiency reaching up to 34% at 670 nm. We also show that MWCNTs covering a quartz substrate still exhibit photocurrent, though well below than that of the MWCNTs coating the silicon substrate. These results suggest that MWCNTs are able to generate photocurrent and that the silicon substrate plays a fundamental role in our planar device. The former effect is particularly interesting because MWCNTs are generally known to mimic the electronic properties of graphite, which does not present any photocurrent generation. On the basis of theoretical calculations revealing a weak metallic character for MWCNTs, we suggest that both metallic and semiconducting nanotubes are able to generate e-h pairs upon illumination. This can be ascribed to the presence of van Hove singularities in the density of states of each single wall carbon nanotube constituting the MWCNT and to the low density of electrons at the Fermi level. Finally, we suggest that though both MWCNTs and Si substrate are involved in the photocurrent generation process, MWCNT film mainly acts as a semitransparent electrode in our silicon-based device.     

High throughput nanofabrication of silicon nanowire and carbon nanotube tips on AFM probes by stencil-deposited catalysts

A new and versatile technique for the wafer scale nanofabrication of silicon nanowire (SiNW) and multiwalled carbon nanotube (MWNT) tips on atomic force microscope (AFM) probes is presented. Catalyst material for the SiNW and MWNT growth was deposited on prefabricated AFM probes using aligned wafer scale nanostencil lithography. Individual vertical SiNWs were grown epitaxially by a catalytic vapor-liquid-solid (VLS) process and MWNTs were grown by a plasma-enhanced chemical vapor (PECVD) process on the AFM probes. The AFM probes were tested for imaging micrometers-deep trenches, where they demonstrated a significantly better performance than commercial high aspect ratio tips. Our method demonstrates a reliable and cost-efficient route toward wafer scale manufacturing of SiNW and MWNT AFM probes.     

Template synthesis and growth mechanism of metal nanowire/carbon nanotube heterojunctions

Copper (Cu) and Cobalt (Co) with remarkable difference in the catalytic activity for the growth of carbon nanotubes (CNTs) have been used to prepare metal-nanowire/CNT heterojunctions. The ordered arrays of Cu nanowire/CNT (CuNW/CNT) and Co nanowire/CNT (CoNW/CNT) heterojunctions were prepared by combining electrochemical deposition and chemical vapor deposition. The interfaces between CNTs and Cu or Co nanowires have been examined and compared. At the interface of CuNW/CNT heterojunction, the tip of CuNW is encapsulated by carbon material (named "cap") and connected the CNT consisting of amorphous carbon (a-C). Two-segment CuNW/amorphous CNT (CuNW/a-CNT) hybrid nanostructure was obtained for the CuNW/CNT heterojunctions due to low catalytic activity of Cu. It is also interesting that a hollow gap was observed between the "cap" and the CuNW. By contrast with the case of Cu, multi-walled CNT (MWCNT) was achieved and no hollow gap was observed at the interface of CoNW/CNT heterojunctions. Three-segment CoNW/MWCNT/a-CNT hybrid nanostructure was observed for the CoNW/CNT heterojunctions because of high catalytic activity of Co. Because no stable copper carbides are observed, we infer that the growth mechanism of CuNW/CNT heterojunctions is different from that of CoNW/CNT. Possible growth models of CuNW/CNT and CoNW/CNT heterojunctions are proposed based on experimental results, respectively.     

Mixed mode brittle fracture in epoxy/multi-walled carbon nanotube nanocomposites

The effects of multi-walled carbon nanotubes (MWNTs) on fracture behavior of epoxy under mixed mode I/II loading have been studied. A number of test specimens based on different contents of MWNTs were prepared and the fracture tests were carried out. The increase in fracture resistance of the nanocomposite depended on the mode mixity. To find the reason, the fracture mechanisms in different modes of fracture were studied by examination of the fracture surfaces. It was found that in addition to the mechanisms, which contribute in mode I fracture, some extra mechanisms participate in mixed mode and mode II loading.     

Static and dynamic mechanical properties of polydimethylsiloxane/carbon nanotube nanocomposites

The purpose of this study is to investigate the static and dynamic mechanical properties of polydimethylsiloxane (PDMS) and the mixture of PDMS and carbon nanotubes. The PDMS/CNT nanocomposites were stirred by an ultrasonic instrument to prevent agglomerations. The tested specimens of nanocomposites were manufactured by using the thermoforming method at 150 °C for 15 min. A micro tensile tester was adopted in this testing system with a maximum load of 500 mN and a crosshead extension of 150 mm. The static elastic modulus can be calculated by means of a tensile test and the average elastic modulus of pure PDMS is 1.65 MPa. In addition, the Nano Bionix tensile tester was also used to perform the dynamic mechanical analysis. Its dynamic frequency range is from 0.1 Hz to 2.5 KHz. The dynamic properties of PDMS/CNT nanocomposites such as storage and loss modulus can be obtained by this system. The storage modulus increased with the CNT content and also with the higher frequencies. Finally, the nanoindentation measurement system was employed to characterize the mechanical properties of PDMS and PDMS/CNTs. The measurement results of elastic modulus by a nanoindentation test have the similar trend with the results obtained by the tensile test method.     

Processing and electrical properties of carbon nanotube/vinyl ester nanocomposites

Vinyl ester resins are often utilized in advanced naval composite structures due to the relatively low viscosity of the resin and the capability to cure at ambient temperatures. These qualities facilitate the production of large naval composite structures using resin infusion techniques. Vinyl ester monomer was synthesized from the epoxy resin to overcome processing challenges associated with volatility of the styrene monomer in vinyl ester resin. In this research we have investigated the use of a calendering approach for dispersion of multi-walled carbon nanotubes in vinyl ester monomer, and the subsequent processing of nanotube/vinyl ester composites. The high aspect ratios of the carbon nanotubes were preserved during processing and enabled the formation of a conductive percolating network at low nanotube concentrations. An electrical percolation threshold below 0.1 wt.% carbon nanotubes in vinyl ester was observed. Formation of percolating carbon nanotube networks at low concentration holds promise for the utilization of carbon nanotubes as in situ sensors for detecting deformation and damage in advanced naval composites.     

Synthesis of polyaniline/multi-walled carbon nanotube nanocomposites in water/oil microemulsion

A water/oil microemulsion system having been successfully used for synthesizing polyaniline(PANi) nanoparticles, was employed for preparing PANi/multi-walled carbon nanotube (MWCNT) nanocomposites via in situ chemical oxidative polymerization. The structures and the electrical property of PANi/MWCNT nanocomposites were also studied. The studies showed that PANi could coat MWCNTs to form nanocables with core-shell structure, and the backbone structure of PANi was not damaged by the introduction of MWCNTs. The conductivities of PANi/MWCNT nanocomposites were higher than that of PANi. Moreover, a model was supposed to be used for describing a PANi/MWCNT nanocable formation by in situ microemulsion polymerization.     

Thermoelectric properties of porous multi-walled carbon nanotube/polyaniline core/shell nanocomposites

Porous polyaniline (PANI)-coated multi-walled carbon nanotube (MWNT) core/shell nanohybrids were fabricated through in situ polymerization and subsequently assembled into macroscopic composites. N(2) adsorption/desorption analysis indicated that the volume of nanopores increased significantly, which could make a significant contribution to phonon scattering. Thermal annealing was also carried out to improve the Seebeck coefficient of the as-produced nanocomposites. The optimal sample showed electrical conductivity of 14.1?S?cm(-1), a Seebeck coefficient of 79.8?μV K(-1) and thermal conductivity of 0.27?W?mK(-1), resulting in a highest figure of merit (ZT) of 0.01 at a very low loading of MWNTs (<1?wt%). These results will provide a potential direction to enhance thermoelectric performance of organic materials and also facilitate the application of organic materials in thermal energy harvesting or cooling.     

Direction sensitive bending sensors based on multi-wall carbon nanotube/epoxy nanocomposites

In the present work, a direction sensitive bending strain sensor consisting of a single block of epoxy/multi-wall carbon nanotube composite was developed. Moreover, the manufacturing could be realized in a straightforward single-step processing route. The directional sensitivity to bending deformations is related to the change in electrical resistance, which becomes positive or negative, depending on the direction of bending deflection. This effect is achieved by generating a gradient in electrical conductivity throughout the material. The resistance versus strain behaviour of these devices is investigated in detail and related to the microstructure of the nanocomposites.